1. Field of the Invention
This invention relates to labels generally, and more specifically but without limitation to deformable labels and to films for making such labels. In one aspect the invention relates to the use of such labels on squeezable or otherwise deformable substrates, where deformability and a resistance of the label to damage from cracking, tearing, creasing, wrinkling or shrinking due to deformation of the underlying substrate is desired. In another aspect the invention relates to such labels which possess the beneficial properties of the known polyethylene labels, but which exhibit improved dispensability and die-cuttability so that the labels may be conveniently applied to deformable substrates with modern labeling equipment.
2. Description of the Prior Art
The shortcomings of paper labels with regard to tearing, wrinkling, creasing, and the like due to age and moisture, or due to a lack of deformability when applied to a deformable substrate, have been well documented in the labeling industry. Over the years, a great deal of effort has been devoted to finding acceptable film facestocks which would overcome these shortcomings and demonstrate a resistance to moisture, to tearing, cracking, creasing, wrinkling, shrinking and so forth. More particularly, substantial efforts have been directed also to finding film facestocks which would have these properties when applied to deformable substrates, particularly as squeezable plastic containers and similar items have become more and more popular with consumers of these items.
The film facestocks which have resulted from these efforts and which have been most dominant in the labeling industry to date are calendered plasticized vinyl (i.e., PVC) and biaxially oriented polyester (i.e., PET), with PVC being primarily used for label applications requiring conformability or deformability. Polyester film facestocks have been used predominately where non-squeezability, durability and metallic brilliance are desired end use characteristics.
With particular regard to the vinyl labels which have been primarily used for deformable substrates in prior years, these demonstrate good squeezability or deformability, good die-cuttability, and adequate dispensability, but are limited in terms of their thickness for use with deformable substrates, have dimensional stability problems in hot-filling or other thermal operations, have a shorter shelf life than is desirable for many uses and present problems of compatibility with the migration of those plasticizers and stabilizers which are required to make PVC pliant enough for use with deformable substrates. Vinyl labels are also currently comparatively more expensive than other common label materials such as polyethylene, implicate environmental concerns over the use of chlorinated materials, and are difficult to recycle with deformable polyethylene substrates, for example.
In more recent times, polystyrene, rubber-modified polystyrene, polypropylene and polyethylene film facestocks have been developed. Each of these known film facestocks also possesses at least one significant disadvantage, however. Polystyrene film facestocks are generally stiff and this quality allows for good machine processability in label application equipment, but limits their utility on deformable substrates. Some use of polystyrene facestocks is possible on mildly deformable substrates where selected adhesives are used, but again this use is limited. Polystyrene films also have a comparatively low tear resistance which can be improved somewhat by rubber modification, and do not generally exhibit a desired exterior durability or solvent resistance.
Polypropylene facestocks are generally dimensionally and chemically stable, but possess a combination of tensile, elongation and tear resistance properties which require a higher die pressure for die cutting than is typically required for even polyethylene labels. Polypropylene labels are also generally not as deformable as is desirable for the bulk of deformable label applications.
Polyethylene labels such as are disclosed in U.S. Pat. No. Re. 32,929 to Ewing have come into use on deformable substrates, as suggested in the referenced patent. Polyethylene as a facestock generally possesses dimensional and chemical stability and is deformable. Polyethylene labels are also printable and possess surface characteristics which make the labels amenable to excellent graphic reproduction. Polyethylene as a roll labelstock, however, is difficult to die cut and to dispense from a liner in labeling equipment because of its elongation and yield characteristics. As a result, efforts have been made to strengthen film and film/paper liners to achieve better die strike resistance and a greater serviceability of these liners at the higher die pressures required to die-cut polyethylene face stock. These efforts have not entirely solved the die-cutting problems posed by polyethylene face stock, however, and they do not adequately address the problems posed by polyethylene labels in terms of their dispensability and handling in high speed labeling equipment.